1. Field of the Invention
This invention relates to a porphyrin derivative compound, and a light emitting device and a display unit which make use of same. More particularly, it relates to a light emitting device and a display unit which have as a constituent material a porphyrin derivative compound which is a porphyrin metal coordination compound or a porphyrin compound and exhibits liquid crystal properties or exhibits phosphorescent or fluorescent light emission properties. This invention also relates to a material having high charge injection performance, utilizing such liquid crystal properties.
2. Related Background Art
In the research on porphyrin derivative compounds, it is hitherto known that porphyrin derivative compounds made to have a long side chain are capable of controlling intermolecular mutual action. For example, it is also known that the porphyrin derivative compounds having a long side chain exhibit a discotic liquid crystal phase. With regard to discotic liquid crystal properties of a porphyrin compound itself, however, the number of compounds exhibiting liquid crystal properties are not large, because it has not been long since the research was commenced.
As an example of such discotic liquid crystal compounds using the porphyrin skeleton, there is a Brian A. Gregg et al paper, Journal of American Chemical Society 1989, 111, 3024-3029, which discloses the structure of compounds using hydrogen (H), zinc (Zn), Copper (Cu), palladium (Pd) or cadmium (Cd) for the central metal and a temperature range in which a discotic liquid crystal phase is exhibited.
In the case of the compound using zinc as the central metal, there is an example in which the temperature at which a phase transition into the discotic liquid crystal phase is caused is at least 61xc2x0 C. In other examples, however, the temperature is 84xc2x0 C. or above, and the compounds that exhibit the discotic liquid crystal phase at around room temperature are still unknown.
An example is also disclosed in which, utilizing a regularity the discotic liquid crystal has, a high mobility has been achieved as an electron mobile layer of an organic EL (organic electroluminescence) device (e.g., Japanese Patent Application Laid-open No. 11-97176). In this example, it is disclosed that, as attempted in solid electrolytes, a structure in which the discotic liquid crystal has been oriented in a specific direction is made up so as to improve charge transportability due to hopping conduction. In the text of this publication, the porphyrin skeleton is described as one of the core structures of compounds for the charge transporting materials. Namely, it is stated that a good charge transport layer can be formed using the discotic liquid crystal. However, the disclosure is limited to the utilization as a charge transport layer having a large charge mobility.
With regard to organic EL devices using porphyrin compounds, the following publications 1 and 2 disclose devices making use of a platinum-porphyrin complex (PtEP) as a light emitting material and show the effectiveness of porphyrin materials as light emitting materials. In particular, devices are studied which utilize not fluorescent light emission via a singlet exciton but phosphorescent light emission via a triplet exciton, and are expected to be effective to improve light emission efficiency.
Publication 1: xe2x80x9cImproved Energy Transfer in Electrophosphorescent Devicesxe2x80x9d (D.F. O""Brien et al., Applied Physics Letters, vol. 74, No. 3, p. 442 (1999)).
Publication 2: xe2x80x9cVery High-Efficiency Green Organic Light-Emitting Devices Based on Electrophosphorescencexe2x80x9d (M.A. Baldo et al., Applied Physics Letters, vol. 75, No. 1, p. 4 (1999)).
Here, the construction of commonly available organic EL devices is shown in FIGS. 3A and 3B. In these devices, a plurality of organic layers are present between a transparent electrode 14 on a transparent substrate 15 and a metal electrode 11. In the device shown in FIG. 3A, the organic layers consist of a light emitting layer 12 and a hole transport layer 13. As the transparent electrode 14, a material having a large work function, such as ITO (indium-tin oxide), is used so that it can be endowed with good hole injection performance from the transparent electrode into the hole transport layer. As the metal electrode 11, a metallic material having a small work function, such as aluminum, magnesium or an alloy formed using these, is used so that it can be endowed with good electron injection performance into the organic layer. These electrodes are formed in a layer thickness of 50 to 200 nm.
In the light emitting layer, an aluminum-quinolinol complex or the like (a typical example is Alq3 shown below) having electron transport properties and light emission properties is used.
In the hole transport layer, a material having electron-donating properties as exemplified by a biphenyldiamine derivative (a typical example is xcex1-NPD shown below) is used.
In the device shown in FIG. 3B, an electron transport layer 16 is further provided between the metal electrode 11 and the light emitting layer 12 which are shown in FIG. 3A. The light emission is separated from the electron transport and hole transport to provide a more effective carrier blocking construction, so that an effective light emission can be performed. As materials for the electron transport layer, an oxadiazole derivative or the like may be used.
In the above publications 1 and 2, such a four-layer organic-layer construction as shown in FIG. 4 is chiefly used. It is constituted of, in this order from the anode side, a hole transport layer 25, a light emitting layer 24, an exciton diffusion preventive layer 23 and an electron transport layer 22. Materials used are carrier transport materials and phosphorescent light emitting materials as shown below.
Alq3: Aluminum-quinolinol complex.
xcex1-NPD:N4,N4xe2x80x2-di-naphthalen-1-yl-N4,N4xe2x80x2-diphenyl-bi phenyl-4,4xe2x80x2-diamine.
CBP: 4,4xe2x80x2-N,Nxe2x80x2-dicarbazole-biphenyl.
BCP: 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline.
PtOEP: platinum-octaethylporphyrin complex.
Ir(ppy)3: Iridium-phenylpyrimidine complex. 
In both the above publications 1 and 2, the device construction which contributes to the high efficiency is the construction that, as host materials, the xcex1-NPD is used in the hole transport layer, the Alq3 in the electron transport layer, the BCP in the exciton diffusion preventive layer and the CBP in the light emitting layer, and the phosphorescent light emitting material PtOEP or Ir(ppy)3 is mixed in a concentration of about 6%.
However, the PtOEP disclosed in the above publication has two carbon atoms in the side chain, and has no liquid crystal properties by itself. It is only used as a light emitting material. Also, its concentration with respect to the host materials is 6%. Accordingly, in order to allow the device to have a higher efficiency, it is expected to be used in a much higher concentration.
As stated above, it is shown that an organic EL device having a high light emission efficiency can be provided using the compound having phosphorescent light emission properties. The device, however, is still not one which can be satisfactory, inclusive of its emission luminance. In general, phosphorescence is often observable at a low temperature of about 77 K, and is not observable at room temperature. The phosphorescent light emitting material or compound herein referred to indicates a compound whose phosphorescent light emission is perceivable within a temperature range near room temperature (0xc2x0 C. or above), required in practical use.
The present invention was made taking into account conventionally known techniques. Accordingly, an object of the present invention is to provide a light emitting device such as an organic EL device, making use of a porphyrin derivative compound.
Another object of the present invention is to provide a porphyrin derivative compound having a high stability as a light emitting material especially used in organic EL devices and as a charge injection material.
Still another object of the present invention is to provide a light emitting device making use of a multifunction porphyrin derivative compound which is light-emissive and especially has phosphorescent light emission properties and liquid crystal properties simultaneously.
A further object of the present invention is to provide a highly luminous and stable light emitting device having a layer containing the above multifunction porphyrin derivative compound, and a display unit having such a device.
The present invention provides a light emitting device comprising a substrate, a pair of electrodes provided on the substrate, and a light emitting portion containing at least one organic compound, provided between the electrodes; the organic compound being a porphyrin derivative compound represented by the following Formula (1) or (2). In particular, it is limited to a compound having a relatively long side chain in which the number of carbon atoms of the side-chain alkyl group is 5 to 20. 
wherein R or Rxe2x80x2 represents a straight-chain or branched alkyl group which may be substituted with a halogen, provided that the number of carbon atoms contained in the alkyl group is 5 to 20 and one methylene group, or two or more methylene groups not adjacent to each other, in the alkyl group may be replaced with xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94; and M is Cr, Ni, Cu, Co, Ru, Rh, Pd, Ir, Pt or Au, which M may be combined with a halogen, an oxygen, xe2x80x94OH or xe2x95x90CO.
In particular, the present invention may be a light emitting device in which M in the compound represented by Formula (1) is Pd, Cu, Pt or Au and M may be combined with a halogen, an oxygen, xe2x80x94OH or xe2x95x90CO.
The present invention also provides a light emitting device comprising a layer containing the porphyrin derivative compound represented by Formula (1) or (2).
The present invention may also preferably be a device in which the layer containing the porphyrin derivative compound represented by Formula (1) or (2) is interposed between two electrodes opposite to each other, and capable of emitting light upon application of a voltage across the electrodes.
The present invention may still also preferably be a device in which the layer containing the porphyrin derivative compound represented by Formula (1) or (2) is interposed between two electrodes opposite to each other, and capable of acting as a charge injection layer upon application of a voltage across the electrodes.
The present invention still also provides a display unit comprising the above light emitting device.